package project20;

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[] grade = new int[5];
        for(int i=0; i<grade.length; i++){
            grade[i] = in.nextInt();
        }

        RR rr = new RT(grade);
        double dd = rr.mark();
        System.out.printf("%.2f",dd);
    }
}
abstract class RR{
    int[] grade;
    public RR(int[] grade){
        this.grade = grade;
    }
    public abstract double mark();
}
class RT extends RR{
    @Override
    public double mark() {
        double sum=0;
        sum=(grade[1]+grade[2]+grade[3])/3;
        return sum;
    }

    public RT(int[] grade) {
        super(grade);
    }
}